Vacuum tube



Jufi gr 18, 1944. J..A. HIPPLE, JR

VACUUM TUBE Filed April 17, 1942 lNVN John A. Hzpple, J2?

WITNESSES:

ATTORN Patented July 18, 1944 VACUUM TUBE John A I-lipple, Jr., ForestHills, Pa., assignor to Westinghouse Electric & Manufacturing Company,East Pittsburgh, Pa., a corporation of Pennsylvania Application April17, 1942, Serial No. 439,345

3 Claims. (Cl. 25027.5)

My invention relates to vacuum tubes and in particular relates to anarrangement for providing an electrostatic shield adjacent the interiorsurface of portions of vacuum tube structures.

For many purposes it is desirable to provide a path for electrons orother charged particles travelling in the interior of the vacuum tubeswhich shall be shielded from the effects of electrical fields set up inthe neighborhood of the tube walls. Thus, for example, massspectrometers are used in which single molecules of various materialsare given electric charges and are then accelerated to considerablevelocities to move through a magnetic field. The latter causes thecharged particles to follow a curved path, the radius of curvature ofwhich is proportional to the square root of the molecular mass. In thisway molecules of different gases, or even isotopes of the same gas,which have different masses are caused to move in paths of differentradius, and this makes it possible to segregate from a mixture ofdifferent molecules anyone set having the same mass. Economy of size inthe vacuum tube employed for this purpose makes it desirable, to

make it in the form of a curved tube of length considerable relative toits diameter. But, however, if the charged molecules were allowed to beacted upon by stray electrical fields emanating from objects in thevicinity of the tube they would be deflected from the curve in whichmolecules of .a particular mass would otherwise be caused to traverse bythe magnetic field and confusion in the observation and segregation ofthe charged molecules would result. The action of the molecules of suchstray electrical fields emanating from objects in the neighborhood ofthe tube can be substantially eliminated if the curved tube along theaction of which the molecules are to travel is given walls having asubstantially electrical conductivity. While it is possible to make suchcurved tubes to form portions of a high vacuum-tight enclosure,difficulty is nevertheless met with from problems from gas occlusion andother causes which make it desirable to employ glass tubes in place ofmetal. However, the problem is then encountered of coating the interiorof the glass wall with some electrical conductor and this problem hasbeen found by experience one of considerable difliculty. A solutionwhich I have found to prove extremely satisfactory is to provide ametallic ribbon having overlapping turns which can be slipped into placeas to form a conductive lining for the interior of the tube wall.-

One object of my invention is accordingly to provide a convenient andsatisfactory method of forming a conductive coating to lie closely adjacent the interior of an insulating tube.

Another object of my invention is to provide an electrostatic shield ofa novel type for the interior of an insulatingtube.

Still another object of my invention is to provide a metallic lining forthe interior of a curved tube of insulating material.

Other objects of my invention will become apparent when reading theaccompanying description when taken in connection with the drawing inwhich Figure 1 is a view partly in elevation and partly in section of avacuum tube embodying a shielding device according to my invention.

Figs. 2 to 5 are detailed views used in illustrating the precisestructure of the shielding device according to my invention; Fig. 2being an elevational view from one side; Fig. 3 an edge view; Fig. 4 anelevational view from the opposite side of the shielding device while inthe course of construction; and Fig. 5 an enlarged section on the lineVV in Fig. 1. 7

Referring in detail to Figure 1, a cylindrical tube I which mayconveniently be made of glass has its axis bent in the arc of a circleand is provided with electrode chambers 2 and 3 at its opposite ends.For purposes of illustration of my invention I apply it to a massspectrometer such as has been referred to above. This consists of acathode chamber 4 containing a suitable thermionic filament 5 or othersource of electrons and having a slit 6 in its wall through which suchelectrons may travel to the exterior of the chamber l. A hollow anode 1attracts electrons emerging through the slit 5 these electrons beingaccelerated by an electrical field due to a difference of potentialmaintained between the chamber 4 and anode l. The anode l is providedwith an aperture or slit 8 aligned with the aperture 6 in chamber 4 andanother electrode 9 which has a horizontal base and a pair of wallsnormal thereto, each such wall being provided with an aperture or slitl0 aligned with the slits 6 and 8. An electrode l I nearly fills thespace between the walls of electrode 9, thus forming a small box throughwhich electrons attracted by anode I pass. The electrode 9 is maintainedat a potential a volt or so lower than the electrode l l and soaccelerates positive gas ions formed in this box downward toward anaperture l2 in the floor of this box.

The tube l is provided with a metalshield or liner I3 which will bedescribed in more detail below, and the end of liner I3 projecting intochamber 2 is capped with a flanged sleeve I4 leaving a slit I5 alignedwith slit I2. The space between the electrodes 9 and II containsmolecules of gas which it is desired to segregate from each other orotherwise test. Electrons emanating through the slit 8 ionize by impactthe molecules just mentioned and a negative potential of about 1000volts on the electrode gives them an acceleration downward. Some ofthese molecules pass through the slit I5 into the main body of the tubeI.

The tube I is maintained at a considerable d gree of vacuum, forexample, l mm. of mercury by a pump connected to a lead-off IS. Thechamber 3 contains a metallic diaphragm I! having an aperture slit I8, asecond metal diaphragm I9 containing a slit 2| and an electrode 22 whichis provided with a lead 23 passing through the tube wall.

The tube thus arranged is placed between the jaws of an electromagnetwhich sets up a field of nearly normal intensity perpendicular to theplane of Fig. 1. The molecules emerging with a considerable velocitythrough the slit I pass into this magnetic field which is made of asconstant an intensity as possible throughout the length of the curvedportion of the tube I. This magnetic field causes the molecules tofollow curved paths, all the molecules of the same molecular weighthaving a path of the same radius, but these radii being different fordifferent groups of molecules which have different molecular Weights. Byproperly adjusting the strength of the field, it is possible to causemolecules of any one selected molecular weight to follow paths having aradius substantially equal to the radius of curvature of the tube I, andmolecules of this particular weight will accordingly pas through theslits I8 and 2| to impinge on the electrode 22. Molecules of othermolecular Weights will either strike the walls of the shield or liner I3and be discharged thereon in a manner about to be described or willstrike portions of the flanged collar I4 and their charges will bereturned by the lead 24 connected by an external circuit to the cathodeof chamber 4.

In order to provide shielding of the greater portion of the tube I fromthe effects of external electrical fields, the tube I is provided with aliner I3 which is made up in the following way. A piece of metal ribbon,for example, a Nichrome V ribbon, 2 mils thick by A" wide and preferablyunannealed, is cut into numerous pieces 3I each having a length slightlygreater than the internal perimeter of tube I. A strap 32 which mat beof Nichrome V wide by 3 mils thick is welded to the successive pieces3|, these overlapping each other as shown in Fig. 3 somewhat like thescales of a fish. The pieces 3I will, for convenience, hereinafter becalled scales. The scales 3I are each slightly reduced in width near thepoint to which it is welded to the strap.

When the welding is complete the scales (H are bent one by one andslipped into a straight glass tube so that they line its walls somewhatas shown in Fig. 5. The natural spring of the metal ribbon tends toforce the scales against the surrounding glass tube. The straight glasstube is of the same internal diameter as the cylindrical portion of thetube I. Before the end chambers of the tube I are fused into place onthe latter the straight glass tube is placed in alignment with one endof the cylindrical portion of tube I, a wire attached to the liner beingfed through the tube I and out its opposite end. By drawing on the wirejust mentioned, it is possible to draw the liner out of the straightglass tube and into the curved cylindrical portion of tube I to form ashield therein. Since the successive scales 3I can slide over each otherat their edges, the liner can bend into conformity with the curvedcylindrical neck of tube I and still form a practically continuousmetallic lining for the latter. Holes 33 are preferably provided inadvance in the position of the liner which will lie opposite the pumplead I5.

I claim as my invention:

1. A vacuum tube comprising a wall portion of insulating material in theform of a cylinder and a metallic lining for said wall portioncomprising a flexible metal strap having fastened thereon a series ofoverlapping metal scales.

2. A vacuum tube comprising a wall portion of insulating material in theform of a cylinder and a metallic lining for said Wall portioncomprising a flexible metal strap carrying a series of overlappingscales of elastic metal.

3. A vacuum tube comprising a wall portion of insulating material in theform of a cylinder having a curved axis and a metallic lining for saidwall portion comprising a flexible metal strap having fastened thereon aseries of overlapping metal scales.

JOHN A. HIPPLE, JR.

